Second pass femtosecond laser for incomplete laser full or partial thickness corneal incisions

ABSTRACT

A method for forming an incision in an eye, the method including performing a first pass of a first laser beam along a path within an eye, wherein after completion of the first pass there exists a residual uncut layer at an anterior surface of a cornea of the eye. The method further including performing a second pass of a second laser beam only along a portion of the path that contains the residual uncut layer, wherein after completion of the second pass, the residual uncut layer is transformed into a full complete through surface incision.

This application claims pursuant to 35 U.S.C. § 119(e) the benefit ofpriority of U.S. provisional application Ser. No. 61/859,737, filed Jul.29, 2013, the entire disclosure of which is-incorporated herein byreference.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to methods and systems for improvingsurgical procedures for improving incomplete full or partial thicknesscorneal incisions.

Discussion of Related Art

Presently, there are a number of surgical methods for correctingmaladies of the eye that involve forming an incision in the cornea ofthe eye. For example, it is known to surgically correct astigmatism byforming limbal relaxing incisions (LRIs) in the eye, wherein such LRIsare generally paired arcuate incisions/cuts formed in the cornea of theeye. In the past, such incisions were formed manually with a fixed orvariable depth blade.

Recently, the practice of making the incisions manually with the abovementioned fixed or variable depth blade is starting to be supplanted byincisions made with a femtosecond laser (Maxine Lipner, EyeWorld,“What's Ahead, Femtosecond technology changing the cataract landscape”,2011 Mar. 24 8:45:27). Such a laser makes incisions by focusingultrashort laser pulses to a very fine focus, causing a plasma mediatedphotodisruption of the tissue at the point of focus. An incision isgenerated by placing a contiguous series of such pulses in a patternthat results in the formation of the desired incision. To make a cornealincision, the point of focus of a femtosecond laser is scanned across aplanar or curved surface within the volume of the target tissue to formthe incision. The beam intensity at the focus is chosen to substantiallyexceed the laser induced optical breakdown threshold of the tissue. Aseach pulse is delivered, a plasma-mediated photo-disruption occurs,vaporizing a miniscule volume of tissue at or near the point of focus. Acavitation bubble subsequently forms near the point of focus which helpscleave the damaged region to form the incision. Using a scanning laserguidance system, laser pulses are placed contiguously in threedimensions across the desired planar or curved surfaces to form theoverall incision. The combined effect of the pattern of pulses is tocleave the tissue at the targeted plane. Arbitrarily complex incisionspatterns can be generated with such lasers. The femtosecond lasers arebelieved to make incisions of a more accurate and consistent depth andof a curvature that more accurately matches the desired arcuate form ofthe incision.

There can be circumstances where the above mentioned femtosecond lasergenerates a low numerical aperture (NA) (or slow F-Theta lens) laserbeam and is paired with a liquid patient interface. A comparison betweena high numerical aperture laser beam 100 that passes through a liquidpatient interface 102 and a low numerical aperture laser beam 104 thatpass through a liquid patient interface 102 is shown in FIGS. 1A and 1B.As shown in FIG. 1A, a high numerical aperture laser beam 100 passesthrough a liquid patient interface 102, resulting in a focused highnumerical aperture laser beam 106. The focused high numerical aperturelaser beam 106 is directed into a portion 108 of the anterior cornealsurface of the cornea of the eye and the beam 106 reaches the rearportion 110 of the portion 108.

As shown in FIG. 1B, a low numerical aperture laser beam 104 passesthrough a liquid patient interface 102, resulting in a focused lownumerical aperture laser beam 112. The focused high numerical aperturelaser beam 112 is directed into a portion of the anterior cornealsurface 108 of the cornea of the eye and the beam 112, the corneal entryincision leaves an unintended residual thin but uncut layer 114 at theanterior corneal surface, such as at the Bowman's membrane of the corneawhich has the stiffest collagen fibers and at the posterior cornealsurface, such as Descemet's membrane which is relatively softer. Theformation of the unintended uncut layer 114 is due to the fact thatthere is a difference at the interface between the optical breakdownthresholds of the epithelium layer of the cornea and the Bowman'smembrane of the cornea at the anterior corneal surface of the cornea ofthe eye. Similarly, an uncut layer at the posterior corneal surface isformed due to the optical breakdown thresholds of the endothelium layerof the cornea and the Descemet's membrane of the cornea at the posteriorcorneal surface of the cornea of the eye. An example of such anunintended uncut layer is shown in FIGS. 2A-B and 3A-B. Note that theunintended uncut layer can be generated in a variety of incisions. Forexample, uncut layers 116, 118 of FIGS. 2A-B and 3A-B can be generatedin a so called Full Thickness corneal Incision (FTI), which is anintended incision from posterior to anterior surface of the cornea aswould be the case for Clear Corneal Incisions (CCIs), paracentesisincisions or Penetrating Keratoplasty (PKP) or other through surfacemodalities. As another example, the uncut layer can be generated in a socalled Partial Thickness Incision (PTI), which intentionally startswithin the stroma and progresses through the anterior surface of the eyeas would be the case for Limbal Relaxing Incision (LRI) and AstigmaticKeratotomy (AK) or other partial thickness modalities. In eitherexample, the presence of the uncut layer results in an incomplete FTI orPTI incision being formed. Note that in either the FTI or PTI incision,the thickness of the residual uncut layer can vary from approximately 10μm to approximately 30 μm, as a function of the numerical aperture andthe output energy of the laser beam.

One shortcoming of the incomplete full or partial thickness cornealincisions of FIGS. 2A-B and 3 A-B is that it can be relatively difficultto locate and open the wound due to the strength of the residual thinlayers 116, 118 left uncut. For human eyes, the residual uncut layersencompass the Bowman's membrane, for partial thickness cornealincisions, and, Bowman's and Descemet's membranes, for full thicknesscorneal incision. Bowman's and Descemet's membranes are the regions ofthe eye structure with the stiffest collagen fibers.

SUMMARY

One aspect of the invention regards a method for forming an incision inan eye, the method including performing a first pass of a first laserbeam along a path within an eye, wherein after completion of the firstpass there exists a residual uncut layer at an anterior surface of acornea of the eye. The method further including performing a second passof a second laser beam only along a portion of the path that containsthe residual uncut layer, wherein after completion of the second pass,the residual uncut layer is transformed into a full complete throughsurface incision.

One or more aspects of the present invention provides for the generationof a full through surface corneal incision in a dependable manner.

One of ordinary skill in the art will recognize, based on the teachingsset forth in these specifications and drawings, that there are variousembodiments and implementations of these teachings to practice thepresent invention. Accordingly, the embodiments in this summary are notmeant to limit these teachings in any way.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A schematically shows a laser beam with a high numerical aperture;

FIG. 1B schematically shows a laser beam with a low numerical aperture;

FIG. 2A is a photograph of a residual thin uncut layer of an intendedfull thickness 1-plane corneal incision;

FIG. 2B is an enlarged portion of the photograph of FIG. 2A;

FIG. 3A is a photograph of a residual thin uncut layer of an intendedfull thickness 3-plane corneal incision;

FIG. 3B is an enlarged portion of the photograph of FIG. 3A;

FIG. 4A schematically shows a first partial incision formed by a firstpossible surgical process in accordance with the present invention;

FIG. 4B schematically shows a first full incision based on the firstpartial incision of FIG. 4A formed by a first possible surgical processin accordance with the present invention;

FIG. 5A schematically shows an embodiment of first pass of a firstfemtosecond laser beam in accordance with a second possible surgicalprocess in accordance with the present invention;

FIG. 5B schematically shows an embodiment of second pass of a secondfemtosecond laser beam in accordance with a second possible surgicalprocess in accordance with the present invention;

FIG. 6A schematically shows an embodiment of first pass of a firstfemtosecond laser beam in accordance with a third possible surgicalprocess in accordance with the present invention;

FIG. 6B schematically shows an embodiment of second pass of a secondfemtosecond laser beam in accordance with a third possible surgicalprocess in accordance with the present invention; and

FIG. 7 shows an embodiment of a surgical device to form the incisions ofFIGS. 4-6 in accordance with the present invention.

DESCRIPTION OF THE DRAWINGS AND THE PREFERRED EMBODIMENTS

In general, the present invention relates to a method of generating acomplete through surface incision of a portion of the eye, such as acomplete incision of a full thickness or partial thickness of the corneaof the eye. An example of a possible partial thickness corneal incision(PTI) of the anterior corneal surface of an eye is shown in FIGS. 4 A-B.Examples of full thickness corneal incisions (FTI) are shown in FIGS.5-6.

In FIG. 4A, an anterior surface 200 and a posterior surface 202 of acornea 204 of an eye are shown. A first pass of a first femtosecondlaser beam is performed in its entirety at a low energy above thephoto-disruption threshold. The first laser beam has an energy in arange of 3 μJ-5 μJ and is a low numerical aperture laser beam thatpasses through a liquid patient interface 201, wherein a low numericalaperture laser beam is used so that the laser focal point will be farenough to reach the lens posterior region and effectively fragmentcataractous materials within the eye. In particular, the first pass ofthe first laser beam begins at a position A within the cornea 204 andmoves linearly toward a position B located past the anterior surface 200and in a chamber filled with a balanced salt solution (BSS). As shown inFIGS. 4A-B, the first pass is along a linear path, wherein a first fullcut 206 is formed. Along the path of the first full cut 206, just belowthe anterior surface of the cornea, an uncut region 210 can remain. Asshown in FIG. 4B, subsequent to the first pass, a second pass 208 of asecond femtosecond laser beam that is a low numerical aperture laserbeam is performed at an energy, such as 6 μJ-14 μJ, which is greater invalue than the energy of the first femtosecond laser beam. The secondpass 208 is performed along a portion of the same linear path as thefirst pass that is near the anterior surface 200 of the cornea 204. Inparticular, the second pass 208 begins at the point C prior to the uncutlayer 210 and ends at position B. Point C is at a pre-programmeddistance 209 below the corneal surface S (200), typically 100-300 μm. Inother words, the second pass 208 includes the uncut layer 210 andextends to the end of the overcut at point B.

Note that prior to executing any incisions, the laser system of FIG. 7uses built in biometry scanning to automatically map the anterior and/orposterior cornea surfaces at the incision site and automaticallydetermines beam path for both the first and second passes. In thepresent case, such automatic mapping and determining would identify thefirst pass path A→B. With the corneal anterior surface S also beingidentified, the system traces back along the path, starting at thesurface S (200), for a predetermined distance, typically 100-300 μm toposition the second pass start point C. After completion of the firstpass, a one-plane partial thickness incision is formed, wherein the term“one-plane” regards the fact that the resultant path from the first passis contained within a single plane. The term “partial thickness” regardsthe fact that the start point A is intentionally within the body of thecornea.

In FIG. 5A, a first pass of a first femtosecond laser beam is performedin its entirety at a low energy above the photo-disruption threshold.The first laser beam is a low numerical aperture laser beam that passesthrough a liquid patient interface 201. In particular, the first passbegins at a position A in the aqueous humor of the eye, moves linearlytoward a position B located in the interior of the cornea 204, and thenchanges direction and moves linearly to position C past the anteriorsurface 200 and in a chamber filled with a balanced salt solution. Thefirst pass is along an angled path, wherein two linear cuts 300 and 304are formed. When attempting to cut across the junction betweendissimilar media (e.g. cornea to BSS or stoma to Bowman's membrane), thedifference in optical breakdown threshold will result in small uncutregions being formed. Just above the posterior corneal surface, insegment 300, an uncut layer 306 remains. Just below the anterior cornealsurface, in the last full cut segment 304, a second uncut layer 308remains.

As shown in FIG. 5B, subsequent to the first pass, a second pass of asecond femtosecond laser beam that is a low numerical aperture laserbeam is performed. Note that the energies of the first and second passesof the first and second laser beams are similar to the energies of thefirst and second laser beams of FIGS. 4A-B. The second pass is performedalong a portion of the same linear path as the first pass that is nearthe anterior surface 200 of the cornea 204. In particular, the secondpass begins at the point D prior to the region of uncut cornea 308 andends at position C so as to define portion 301. In other words, thesecond pass includes the uncut layer 308.

Note that prior to executing any incisions, the laser system of FIG. 7uses built in biometry scanning to automatically map the anterior and/orposterior cornea surfaces at the incision site and automaticallydetermines beam path for both the first and second passes. In thepresent case, such automatic mapping and determining would identify thefirst pass path A→B→C. With the corneal anterior surface S (200) alsobeing identified, the system traces back along the path S→B→A, startingat the surface S, for a predetermined distance, typically 100-300 μm, toposition the second pass start point D. The second pass path is alsodefined as D→B→C. Should the programmed length of the second pass besuch that D lies on the segment S→B, then the second pass will be simplydefined by the linear path D→S.

Note that there is no need for a second pass at the uncut layer 306,since the Descement membrane's stiffness is such that the thin uncutlayer of the uncut layer 306 will be broken naturally from structuralweakness and the residual heat emanating from the laser beam's upwarddisplacement in the aqueous humor of the eye.

After completion of both passes, a two-plane full thickness incision isformed, wherein the term “two-plane” regards the fact that the resultantincision forms two planes. The term “full thickness” regards the factthat the resultant incision intentionally cuts from the posterior toanterior surface of the cornea.

In FIG. 6A, a first pass of a first femtosecond laser beam is performedin its entirety at a low energy above the photo-disruption threshold.The laser beam is a low numerical aperture laser beam that passesthrough a liquid patient interface 201. In particular, the first passbegins at a position A in the aqueous humor of the eye, moves linearlytoward a position B located in the interior of the cornea 204, and thenchanges direction and moves linearly to position C. Next, the laser beamchanges direction and moves linearly past the anterior surface 200 to aposition D in a chamber filled with a balanced salt solution. The firstpass is along a zigzag angled path, wherein linear full cuts 400,402 and406 are formed. Just above the posterior corneal surface, in segment400, an uncut layer 404 remains. Just below the anterior cornealsurface, in the last full cut segment 406, a second uncut layer 408remains.

As shown in FIG. 6B, subsequent to the first pass, a second pass of asecond femtosecond laser beam that is a low numerical aperture laserbeam is performed. Note that the energies of the first and second passesof the first and second laser beams are similar to the energies of thefirst and second laser beams of FIGS. 4A-B. The second pass is performedalong a portion of the same linear path as the first pass that is nearthe anterior surface 200 of the cornea 204. In particular, the secondpass begins at the point E prior to the region of uncut cornea 408 andends at position D. In other words, the second pass includes the uncutlayer 408. Note that prior to executing any incisions the laser systemof FIG. 7 uses built in biometry scanning to automatically map theanterior and/or posterior cornea surfaces at the incision site andautomatically determines the second pass path. In the present case, suchautomatic mapping and determining would identify the first pass pathA→B→C→D. With the corneal anterior surface S being identified, thesystem traces back along the first pass path, starting at the surface S,for a predetermined distance, typically 100-300 μm to position thesecond pass start point E. The system then performs a second pass alongthe path E→C→D. Note that if the length S→C is greater than the secondpass length then the second pass will be performed along a single linearpath E→D.

Note that there is no need for a second pass at the uncut layer 404,since the Descement membrane's stiffness is such that the thin uncutlayer of the uncut layer 404 will be broken naturally from structuralweakness and the residual heat emanating from the upstream laser beam inthe aqueous humor of the eye.

After completion of both passes, a three-plane full thickness incisionis formed, wherein the term “three-plane” regards the fact that theresultant incision forms three planes. The term “full thickness” regardsthe fact that the resultant incision intentionally cuts from theposterior to anterior surface of the cornea.

Note that there are several principles involved regarding the use of asecond pass on the incomplete cuts at the anterior surface of the corneafor the incisions shown in FIGS. 4A-B, 5A-B and 6A-B. First, the secondpass results in increased visibility of the incision entrance for thesurgeon. Second, the stiffness of the Bowman's membrane is much greaterthan that of the Descement's membrane and so structural weakness of theBowman's membrane and residual heat from the air bubbles produced byphotodisruption in the balanced salt solution will not be sufficient inthemselves to break the uncut layer at the anterior surface of thecornea. Thus, a second pass of the laser beam is necessary break theuncut layer. On a related point, the present two-pass technique avoidsthe use of just a single pass of a laser beam to form a full cut at theanterior surface of the cornea. Most nerves reside between theendothelial cells and the Bowman's membrane and so a single pass lasertechnique could induce unwarranted pain to the patient due to theaggravation of the nerves by the laser. In contrast, the presentlydescribed two pass technique results in the further softening of theresidual uncut layers and so helps to ease the opening of the wound.

In order to form the first and second pass patterns of FIGS. 4-6, alaser system is provided as shown in FIG. 7 and as described in U.S.patent application Ser. No. 12/831,783, the entire contents of which areincorporated herein by reference. In particular, the laser systemincludes a treatment laser 501 which should provide a beam 504. The beamshould be of a short pulse width, together with the energy and beamsize, to produce photodisruption. Thus, as used herein, the term lasershot or shot refers to a laser beam pulse delivered to a location thatresults in photodisruption. As used herein, the term photodisruptionessentially refers to the conversion of matter to a gas by the laser,with accompanying shock wave and cavitation bubble. The termphotodisruption has also been generally referred to as Laser InducedOptical Breakdown (LIOB). In particular, wavelengths of about 300 nm to2500 nm may be employed. Pulse widths from about 1 femtosecond to 100picoseconds may be employed. Energies from about a 1 nanojoule to 1millijoule may be employed. The pulse rate (also referred to as pulserepetition frequency (PRF) and pulses per second measured in Hertz) maybe from about 1 KHz to several GHz. Generally, lower pulse ratescorrespond to higher pulse energy in commercial laser devices. A widevariety of laser types may be used to cause photodisruption of oculartissues, dependent upon pulse width and energy density. Thus, examplesof such lasers are disclosed in U.S. Patent Application Publication No.2007/084694 A2 and WO 2007/084627A2, the entire contents of each ofwhich are incorporated herein by reference. These and other similarlasers may be used as therapeutic lasers. For procedures on the corneathe same type of therapeutic laser as described herein may be used, withthe energy and focal point being selected to perform the desiredprocedure.

In general, the optics 502 for delivering the laser beam 504 to thestructures of the eye should be capable of providing a series of shotsto the natural lens in a precise and predetermined pattern in the x, yand z dimension. The z dimension as used herein refers to that dimensionwhich has an axis that corresponds to, or is essentially parallel withthe anterior to posterior (AP) axis of the eye. The optics should alsoprovide a predetermined beam spot size to cause photodisruption with thelaser energy reaching the structure of the eye intended to be cut.

In general, the control system 503 for delivering the laser beam 504 maybe any computer, controller, and/or software hardware combination thatis capable of selecting and controlling x-y-z scanning parameters andlaser firing. These components may typically be associated at least inpart with circuit boards that interface to the x-y scanner, the zfocusing device and/or the laser. The control system may also, but doesnot necessarily, have the further capabilities of controlling the othercomponents of the system, as well as, maintaining data, obtaining dataand performing calculations. Thus, the control system may contain theprograms that direct the laser through one or more laser shot patterns.Similarly, the control system may be capable of processing data from theslit scanned laser and/or from a separate controller for the slitscanned laser system.

The laser optics 502 for delivering the laser beam 504 includes a beamexpander telescope 505, a z focus mechanism 506, a beam combiner 507, anx-y scanner 508, and focusing optics 509. There is further providedrelay optics 510, camera optics 511, which include a zoom, and a firstced camera 512.

Optical images of the eye 514 and in particular optical images of thenatural lens of the eye 520 are conveyed along a path 513. This path 513follows the same path as the laser beam 504 from the natural lensthrough the laser patient interface 516, the focusing optics 509, thex-y scanner 508 and the beam combiner 507. There is further provided alaser patient interface 516, a structured light source 517 and astructured light camera 518, including a lens. Examples of patientinterface and related apparatus that are useful with the present systemare provided in regular and provisional U.S. patent application Ser. No.12/509,021 and Ser. No. 61/228,457, wherein each was filed on the sameday as the present application and wherein the entire disclosures ofeach of which are incorporated herein by reference.

The structured light source 517 may be a slit illumination havingfocusing and structured light projection optics, such as aSchafter+Kirchhoff Laser Macro Line Generator Model 13LTM+90CM, (Type13LTM-250S-41+90CM-M60-780-5-Y03-C-6) or a StockerYale ModelSNF-501L-660-20-5, which is also referred to as a slit scanned laser. Inthis embodiment the structured illumination source 517 also includesslit scanning means 519. The operation of using a scanned slitillumination is described in described in U.S. patent application Ser.No. 12/831,783.

The images from the camera 518 may be conveyed to the controller 503 forprocessing and further use in the operation of the system. They may alsobe sent to a separate processor and/or controller, which in turncommunicates with the controller 503. The structured light source 517,the camera 518 and the slit scanning means 519 include a means fordetermining the position and apex of the lens in relation to the lasersystem. Based at least on part from the determined position and apex ofthe lens, the scanning of the laser beam 504 upon the eye 520 can becontrolled by controller 503. For example, to make a corneal incision, apoint of focus of a laser, such as a femtosecond laser, generates a lownumerical aperture beam that passes through a liquid patient interface201 that adjoins the eye and is scanned during a first pass across aplanar or curved surface within the volume of the target tissue to formthe incision. The beam is a low numerical aperture beam and has anintensity at focus is chosen to be at a low energy that just exceeds thelaser induced optical breakdown threshold of the tissue. As each pulseis delivered, a plasma-mediated photo-disruption occurs, vaporizing aminiscule volume of tissue at or near the point of focus. A cavitationbubble subsequently forms near the point of focus which helps cleave thedamaged region to form the incision. Using a scanning laser guidancesystem as shown in FIG. 6, laser pulses are placed contiguously in threedimensions across the desired planar or curved surfaces to form theoverall incision. During the first pass of the laser beam, a partial cutwill result in the manner discussed with respect to FIGS. 2A-B. In thissituation, a second pass of a laser beam is automatically performedshortly after completion of the first pass wherein scanning of a secondlow numerical aperture laser beam that passes through the liquid patientinterface is performed at a higher energy and scanning speed whencompared with the first pass. The second pass involves having the laserbeam follow a portion of the same path as followed by the laser beam ofthe first pass near the anterior surface of the cornea. At least in thecase of making an incision into an anterior portion of the cornea, thelaser parameters, including energy and scanning speed, are optimized tocut through the denser cells without compromising effectiveness withinthe stroma. For example, during the first pass, the XY spacing betweenshots ranges from 4 to 8 μm, the Z spacing of the shots ranges from 4 to5 m, the energy ranges from 3 to 5 J and the pulse repetition frequencyis approximately 80 kHz. During the second pass, the XY spacing betweenshots ranges from 6 to 10 μm, the Z spacing of the shots ranges from 4to 8 μm, the energy ranges from 6 to 14 ρJ and the pulse repetitionfrequency is approximately 80 kHz. After scanning of the second pass,the partial cut near the anterior surface of the cornea has evolved intoa full cut. Note that in the case of making an incision at the anteriorsurface portion of the cornea, the incision extends only minimally intothe stroma. Note that the above mentioned two pass process can beapplied to form the incisions shown in FIGS. 4-6.

From the foregoing description, one skilled in the art can readilyascertain the essential characteristics of this invention, and withoutdeparting from the spirit and scope thereof, can make various changesand/or modifications of the invention to adapt it to various usages andconditions.

1-14. (canceled)
 15. A method for forming an incision in an eye, themethod comprising: performing a first pass of a first laser beam along afirst portion of a path within the cornea of an eye, the pass startingfrom a point within the cornea and moving toward the anterior surface ofthe cornea; thereby forming an incision within the cornea; wherein aftercompletion of the first pass there exists a residual uncut layer at theanterior surface of the cornea, wherein the residual layer includesBowman's membrane; performing a second pass of a second laser beam alonga second portion of the path; the first and second portions of the pathat least partially overlapping; wherein the second portion of the pathcontains the residual uncut layer, wherein after completion of saidsecond pass, the residual uncut layer is transformed into a fullcomplete through surface incision.
 16. The method of claim 15, whereinsaid first laser beam has a low numerical aperture and passes through aliquid-filled patient interface before penetrating said eye, and whereinsaid residual uncut layer is the result of said first laser beam passingthrough said liquid-filled patient interface.
 17. The method of claim15, wherein said path is formed in a cornea of an eye.
 18. The method ofclaim 15, wherein said first laser beam has a different energy than saidsecond laser beam.
 19. The method of claim 15, wherein said first laserbeam is at a first energy of 3 μJ to 5 μJ, wherein the first energyexceeds a photodisruption threshold and said second laser beam is at asecond energy that is higher than the first energy
 20. The method ofclaim 15, wherein said first laser beam is scanned along said path at adifferent rate than said second laser beam is scanned along said portionof said path that contains said partial thickness incision.
 21. Themethod of claim 15, wherein said path is a linear path and said portionof said path that contains said residual uncut layer is linear.
 22. Themethod of claim 15, wherein said path is an angular path and saidportion of said path that contains said residual uncut layer is linear.23. The method of claim 15, wherein said path is an angular path andsaid portion of said path that contains said residual uncut layer isangular.
 24. The method of claim 15, wherein said first laser beam has apulse width that is less than one femtosecond and said second laser beamhas a pulse width that is less than one femtosecond.
 25. The method ofclaim 15, wherein after completion of said second pass, a full thicknesscorneal incision is formed.
 26. The method of claim 15, wherein aftercompletion of said second pass, a partial thickness corneal incision isformed.